Excessive body weight is becoming a concern around the world, for example, over half of the American adult population is considered to be overweight or obese. Being overweight is associated with several conditions or chronic diseases such as hypertension, elevated cholesterol, type 2 diabetes, stroke, osteoarthritis, and sleep apnea. Economically, the annual costs for excessive body weight on medical expenses and lost income is approximately 70 billion dollars, in the United States alone.
There are many factors that affect body weight or influence a person's ability to lose weight. Many diet programs focus solely on energy (kcals) intake yet the body responds differently to macronutrients (i.e. with simple carbohydrates, the insulin response triggers the body to store fat). Furthermore as dietary energy levels decrease, the body meets its energy demands through utilizing protein and lean body tissue as its primary energy source. Therefore, as a person loses weight there can be a significant loss of muscle which can adversely affect body weight maintenance over the long term. Moreover, if the dieter ceases the diet and gains back some or all of the weight lost, it will typically be as fat. Thus, the dieter may find themselves in an even worse physical condition than when they started the diet as they now weigh the same as before, but have a higher percentage of body fat and lower percentage of muscle.